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Purpose The purpose of this paper is to solve the reactive power adjustment and the overvoltage suppression problems in the extra high voltage (EHV) long distance grid, which often appears transient overvoltage, light load loss and other issues. Design/methodology/approach One 800 kV EHV magnetically saturation controllable reactor (MSCR) used self-power supply control system is designed. The structure and the working mechanism of the novel MSCR are analyzed in detail. Then the control and capacity step adjustment characteristics are obtained by experiments. The harmonic characteristic is studied by theoretical analysis and low voltage test. Findings To solve the problem of harmonics in the working current of nets windings, the fifth and the seventh filers are equipped between the compensation windings and the control system. The effectiveness of the harmonic suppression method is proved by simulation and experiments. Originality/value It proves that the 800 kV EHV MSCR design in this paper can achieve the purpose of the reactive power continuous linear adjustment, and the capacity adjustment is sensitive. After filtering, the harmonics level of the working current meets the standard of the EHV grid.

The dielectric parameters of oil-immersed insulation paper, semi-conductive paper and mineral oil were measured at different temperature. The quantitative analysis about the influence of the equalizing cage density on the Inverted-type Oil-immersed Current Transformer (IOCT) electric field distribution was studied, and the temperature dependence of the insulation material dielectric parameters were taken into consideration. In high temperature conditions, the oil-paper damage of IOCT insulation system is generally not caused by electric breakdown but heat aging. The maximum electric field strength of oil-paper I is approximately reduced by 12.84%, and that of the oil-paper II is reduced by 0.35%, after the equalizing cage density is increased. The increasing of the equalizing cage density will be beneficial to the electric field equidistribution of the IOCT insulation system.